This invention relates to an injection unit for injection molding, and more particularly to an injection unit for the hot runner molding.
Conventionally, for the purpose of maintaining, in the injection molding of plastic, a sprue and runner molded integrally with a plastic molding and disused after released therefrom in a fused condition to attain the effective utilization of plastic, the injection molding method using a hot runner is widely adopted. In the hot runner, there is known the type wherein, for the purpose of maintaining a resin within the runner in a fused condition, cartridge heaters are disposed surrounding the runner; and band heaters are mounted surrounding the nozzle portion of the runner connecting to the gate of the moldings. Such construction, however, has the drawback that a sufficient control can not be made of the plastic injection from the nozzle. For this reason, a large number of injection units adapted to close the injection nozzle using valve means have been proposed. But any of these injection units is complicated in construction and renders it difficult to control the injection with precision.